From 36e66c554b5c6a9d17a229faca7a61693527b0bd Mon Sep 17 00:00:00 2001 From: Alexander Duyck Date: Mon, 6 Apr 2020 20:04:56 -0700 Subject: mm: introduce Reported pages In order to pave the way for free page reporting in virtualized environments we will need a way to get pages out of the free lists and identify those pages after they have been returned. To accomplish this, this patch adds the concept of a Reported Buddy, which is essentially meant to just be the Uptodate flag used in conjunction with the Buddy page type. To prevent the reported pages from leaking outside of the buddy lists I added a check to clear the PageReported bit in the del_page_from_free_list function. As a result any reported page that is split, merged, or allocated will have the flag cleared prior to the PageBuddy value being cleared. The process for reporting pages is fairly simple. Once we free a page that meets the minimum order for page reporting we will schedule a worker thread to start 2s or more in the future. That worker thread will begin working from the lowest supported page reporting order up to MAX_ORDER - 1 pulling unreported pages from the free list and storing them in the scatterlist. When processing each individual free list it is necessary for the worker thread to release the zone lock when it needs to stop and report the full scatterlist of pages. To reduce the work of the next iteration the worker thread will rotate the free list so that the first unreported page in the free list becomes the first entry in the list. It will then call a reporting function providing information on how many entries are in the scatterlist. Once the function completes it will return the pages to the free area from which they were allocated and start over pulling more pages from the free areas until there are no longer enough pages to report on to keep the worker busy, or we have processed as many pages as were contained in the free area when we started processing the list. The worker thread will work in a round-robin fashion making its way though each zone requesting reporting, and through each reportable free list within that zone. Once all free areas within the zone have been processed it will check to see if there have been any requests for reporting while it was processing. If so it will reschedule the worker thread to start up again in roughly 2s and exit. Signed-off-by: Alexander Duyck Signed-off-by: Andrew Morton Acked-by: Mel Gorman Cc: Andrea Arcangeli Cc: Dan Williams Cc: Dave Hansen Cc: David Hildenbrand Cc: Konrad Rzeszutek Wilk Cc: Luiz Capitulino Cc: Matthew Wilcox Cc: Michael S. Tsirkin Cc: Michal Hocko Cc: Nitesh Narayan Lal Cc: Oscar Salvador Cc: Pankaj Gupta Cc: Paolo Bonzini Cc: Rik van Riel Cc: Vlastimil Babka Cc: Wei Wang Cc: Yang Zhang Cc: wei qi Link: http://lkml.kernel.org/r/20200211224635.29318.19750.stgit@localhost.localdomain Signed-off-by: Linus Torvalds --- mm/Kconfig | 11 +++++++++++ 1 file changed, 11 insertions(+) (limited to 'mm/Kconfig') diff --git a/mm/Kconfig b/mm/Kconfig index 211a70e8d5cf..d286dc54458c 100644 --- a/mm/Kconfig +++ b/mm/Kconfig @@ -236,6 +236,17 @@ config COMPACTION it and then we would be really interested to hear about that at linux-mm@kvack.org. +# +# support for free page reporting +config PAGE_REPORTING + bool "Free page reporting" + def_bool n + help + Free page reporting allows for the incremental acquisition of + free pages from the buddy allocator for the purpose of reporting + those pages to another entity, such as a hypervisor, so that the + memory can be freed within the host for other uses. + # # support for page migration # -- cgit v1.2.3